Automated test equipment, or ATE, provides semiconductor manufacturers the capability of individually testing each and every semiconductor device fabricated during production. The testing is usually carried out at both the wafer level and the packaged-device level to ensure operability of the devices before reaching the marketplace.
Modern semiconductor devices typically have anywhere from thirty-two to over one-thousand pins, generally requiring a corresponding number of channels in the semiconductor tester to thoroughly verify the operation of the device. Each channel usually comprises a signal path including the necessary pin electronics for sending and/or receiving test signals to and from a pin on the DUT. In conventional testers, to maximize component density and minimize the size of the tester, the channels are often formed on printed circuit boards resident within a testhead. The testhead is separated from the main body of the tester for coupling to the DUTs that are mounted on a prober or handler.
Because of the relatively high concentration of circuit boards within a conventional testhead, specialized cooling systems are generally employed to maintain a stable thermal environment. Some prior systems have employed air cooling, which typically includes elaborate ducting that takes up valuable space within the testhead. As a result, these air cooling systems contribute to a larger overall footprint for the tester. Moreover, because the airflow must overcome the resistive effects of ducting, nozzles and the uneven shapes and surfaces of the boards, the air cooled systems tend to not be as efficient as desired.
Other approaches have included liquid cooling systems that circulate a fluid, typically water, from a liquid cooler, i.e. a refrigeration unit, and past the heat producing electronic components, i.e. microchips, and back to the cooler. Liquid is passed through cooling blocks, which are attached to the electronic components, to allow the heat to transfer from the components to the liquid. In these systems, the cooling blocks are attached to one another with tubes or hoses, in series to form a single path or channel for the liquid to pass though. That is, these systems flow the liquid from the cooling unit, which typically includes a pump, to a first cooling block, where heat is transferred from the electronic component, which the cooling block is mounted on, into the liquid. Then the liquid leaves the first cooling block through a connecting tube to a second cooling block, where heat is again transferred into the liquid from another electronic component. The liquid continues to move through a series of cooling blocks in succession, having heat transferred into it at each cooling block, until it returns to the cooling unit.
Because the liquid is heated each time it passes through a cooling block, the temperature varies unpredictably with each cooling block in the series of cooling blocks. That is, with such cooling systems each electronic component will be operating at a different temperature, with the temperature rising along the path of the liquid through the cooling blocks.
Lately, the trend has been with modern electronic components, especially those used in current automated test equipment, of becoming more and more sensitive to temperature levels, and any fluctuations thereof. To optimize performance of these components and to obtain uniform performance with among a set of components, a stable and common temperature level is desired across all the components. This is difficult to achieve with the variable liquid temperatures provided by the prior liquid cooling systems.
Therefore, a need exists for a cooling system that provides an uniform, predictable and consistent cooling environment for each of the electronic components being cooled. Such a system should allow for ease of access to reduce the time needed for servicing and, as a result, minimize overall equipment downtime.